What is the volume of 0.20 moles of helium at STP?
A) 0.22 liters
B) 0.45 liters
C) 4.5 liters
D) 9.0 liters

The volume of 0.20 moles of helium at STP is 4.5 liters.

Explanation:

Given:

Number of moles  = 0.20 moles

To Find:

The volume of Helium at STP =?

Solution:

According to ideal gas law

PV = nRT

where

P is pressure,  

V  is volume,  

n  is the number of moles  

R  is the gas constant, and  

T  is temperature in Kelvin.

The question already gives us the values for  p  and  T ,because helium is at STP. This means that temperature is  273.15 K  and pressure is  1 atm .

We also already know the gas constant. In our case, we'll use the value of  

0.08206 L atm/K mol  since these units fit the units of our given values the best

On substituting these values we get

V =  4.5 Liters